1. Field of the Invention
The present invention is related to a device for flexible guiding of conveyed flat products, particularly printed products, when conveyed from a folding apparatus to further processing lines.
2. State of the Art
In conventional web delivery systems, when a signature impacts a fixed guide, a large impact force is required to abruptly change the signature's direction. If the magnitude of this impact force is large enough, it can scrape, scratch and mark a signature's surface, causing unwanted damage. In addition, ink that may have been printed onto a signature can be scraped off of the signature as it is being transported along the guide. As a result, scraped ink can build on the guide and, in turn, be transferred back onto another signature, resulting in improper marking of that signature.
As shown in European Patent No. EP 0 662 439 B1, a pneumatic sheet guiding device is arranged in a sheet fed letterpress along a sheet conveying path. The pneumatic sheet feeding device comprises an upper part with openings to discharge blown air and an extensible lower part peripherally connected to the upper part. The upper part and the lower part form a cavity that is impermeable to air. The upper part and the lower part are both comprised of a flexible material, however, the lower part is considerably more flexible than the upper part. The upper part is bendable and the lower part is extendible such that when air is blown into the cavity formed between the upper part and lower part, an air pocket is formed which allows the lower part to change to a different curvature.
A problem occurs upon transfer of sheet-like material, such as signatures, and the changing of the direction of signatures while being conveyed at high speeds. Contact and shear forces exerted upon the signatures to be conveyed may have a damaging effect. The contact force is in a direction normal to the guide while the shear force is in a direction of the signature's motion.
Typically, a constant force exerted by one body on another in a collision results in a sharply rising force to a very large value in a relatively short period of time. The product of the average force (F.sub.average) and the time over which the force acts (.DELTA.t) constitute the signature's force impulse (i.e., force versus time curve), and thus the signature's momentum. Accordingly, there is a need to reduce the effect of impact forces on a signature being conveyed along a path.